Fluorinated analogs of tyramine, dopamine, melatonin, and serotonin (5-hydroxytryptamine) have been synthesized by novel chemical methods, including photo-chemical transformation. Studies with these analogs have provided significant information on the importance of substrate lipophilicity to MAO-A and MAO-B, the role of zwitterionic character in the transport of serotonin, the role of phenolic pK in the activities of dopamine, and the sites of storage of serotonin in tissues. BIBLIOGRAPHIC REFERENCES: Kirk, K.L.: Photochemistry of Diazonium Salts. IV. Synthesis of Ring-fluorinated Tyramines and Dopamines. J. Org. Chem., 41, 2373-2376 (1977). Kirk, K.L.: Synthesis of Ring-fluorinated Serotonins and Melatonins. J. Heterocyclic Chem., 13, 1253-1256 (1977).